This scenario presents a risk that primarily impacts availability, which is one of the three core information security principles alongside confidentiality and integrity. Relying on a single server to manage all incoming traffic introduces a single point of failure, meaning that if the server fails, services become unavailable.

From an ISO/IEC 27001 perspective, this is clearly a risk, not merely a misconfiguration or a system error. A risk exists because there is a reasonable likelihood that the server could fail and a significant impact if it does, namely service disruption. ISO/IEC 27001 clause 6.1.2 requires organizations to identify such risks that could affect the availability of information and services.

Option B is incorrect because while misconfiguration can cause outages, the scenario does not describe an incorrect configuration; it describes an architectural dependency. Option C is incorrect because authentication is not the primary concern; the issue affects the ability to deliver services at all, regardless of user authentication.

Availability is explicitly addressed in ISO/IEC 27002:2022 through controls such as redundancy and capacity management. The absence of redundancy increases availability risk. Therefore, the scenario correctly represents a risk impacting availability, making option A the best answer.